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Excessive performance/system issues with GSHP

Ground Source Heat Pump (GSHPs)

Last Post by greenlight 9 months ago

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didjerama_uk

(@didjerama_uk)

Active Member Member

Joined: 1 year ago

Posts: 4

Topic starter 27/11/2024 9:19 am

Hi,

We have moved into a property with an Ecoforest GSHP (installed 7years ago) earlier this year and we are having problems with the performance and the cost of running the GHSP as our primary heat source.

After moving into the property we have found out that the GSHP was using 30KW a day just to keep the buffer tank close to the set point without a demand for Central heating being needed. (How the system was running when we moved in).

We have then have the GHSP unit diagnosed having low refringent (less then 10% was in the unit) and repaired due to 5 leaks being found on the device.

We have some serious concerns about the design of the install. One of our concerns is over the suitability of the ground loops. We are seeing low ground temperatures very early in the winter, poor system performance, and very high running costs.

For example, the house is 175m2 (90's build) - we are seeing energy usage around 50+kw each day to keep the house at 16.5/17C. We have the heat pump set to be on all the time, with the thermostat calling for heat whenever the temp drops below the set point of the thermostat. It wasn't uncommon last week in the cold to find the GHSP had consumed 30KW of electric before 12pm.. Yet it was taking the GSHP 4-5hours to return the house from 16.5C to 17C.

The system design includes a buffer tank which is fed from the GSHP. This seems to be a very old copper based tank, bare copper on the bottom which touches the floor (the rest has some insultation). However as this is an existing install we don't have any design documents or calculations for the designed heat loss of the house etc. We do however have the MCS certificate.

As you can imagine we have some concerns over how to resolve this as we believe that a GSHP heating solution should be better than how ours is currently configured.

Example of some of the stats (last weekend) from the GHSP:

Brine in: 4.5C

Brine out: 1.9C

Outside air temp: 9.8C

Heat out: 44.1C

Heat In: 39.9C

Buffer set point 47C.

As we don't have any documents for the brine circuit we have doubts around the brine circuit performance as i'm correct in thinking the brine circuit temps should be constant? We currently notice the brine temps stay very close to the outdoor air temps.

Happy to provide any more information but we wonder what our next steps would be. We asked the orginal installers to provide a service of the unit a few months ago which is why the fault was found however they was unable to fix this as they wasn't F-Gas engineers and we have lost confident that they would be able to provide a system mindset to trying to resolve our issues.

Thanks

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Toodles

(@toodles)

Illustrious Member Contributor

Joined: 3 years ago

Posts: 2360

27/11/2024 5:06 pm

I know the cube route of sod all about GSHP as such but, from what you have written, I think you might be wise to investigate how deep in the ground the loops have been buried. I say this as it sounds as though the difference in the water temperature and the ground’s surface are minimal whereas there should be a marked difference as the ground should not be chilling as your loop suggests it is. Just my £0.1 worth. Toodles.

Toodles, heats his home with cold draughts and cooks food with magnets.

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Graham S

(@graham-s)

New Member Member

Joined: 4 years ago

Posts: 4

27/11/2024 10:00 pm

Hi,

I don't claim to be an expert but I do have a GSHP and happy to share my experience. Firstly yes, 50kWh to maintain 17C sounds pretty inefficient. I can heat our old stone walled cottage to a constant 22 - 23C (yes, I know, but it's a holiday let and that's what paying guests seem to expect!) for about 40 - 50kWh during the recent cold snap. But you don't say anything about your house - heat emitters? insulation? Etc i.e. it should well be factors or 5 than the heat pump itself causing the poor performance.

The behind temps look OK 'ish: you should be seeing about 4C difference between in and out. For comparison last Sunday I was seeing:

Brine in: 5.5C

Brine out: 1.3C

Outside air temp: 11CC

Heat out: 39.1C

Heat In: 36.3C

So, not that dissimilar to what you were seeing, which makes me think it might be more to do with your building fabric? We have insulated floor slabs with underfloor heating, oversized radiators upstairs, lime/hemp insulated walls, sheeps wool in the loft, lots of draught proofing and double glazing throughout...

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didjerama_uk

(@didjerama_uk)

Active Member Member

Joined: 1 year ago

Posts: 4

Topic starter 28/11/2024 10:39 am

@toodles Thanks - Yeah we had wondered. We don't have any of the technical drawings or calculations of the brine circuit. However we do know that the circuit is nearly 20 years old. Our understanding from reading is that we'd expect the brine circuit to be at a higher temp generally. However without the calculations its a bit difficult to understand the design of the brine circuit..

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didjerama_uk

(@didjerama_uk)

Active Member Member

Joined: 1 year ago

Posts: 4

Topic starter 28/11/2024 10:42 am

@graham-s Really useful to know, thank you. We have cavity wall insulation, suspended ground floor with no insultation, double glazing etc. however we aren't sure what the speciation of the system is designed for (in terms of heat loss). Our main concern is the buffer tank as it really not holding the heat and heating circuit seems to be lower than the set point of the buffer tank..

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robl

(@robl)

Honorable Member Member

Joined: 4 years ago

Posts: 207

28/11/2024 3:17 pm

We have a small gshp, and in very cold weather the glycol out can be 0C, sometimes even -6C by the end of winter in a cold snap. Our rads run at 32C though, quite a bit more efficient than your buffer at 47C. It’s that deltaT that predicts the COP generally - attached a graph for our system, for interest. (Blue is hot water, orange heating).
How do you know the consumed electricity - ideally a mid certified meter placed in line with the gshp unit.

Do you have an EPC for the property? That will give estimated yearly energy demand.

This post was modified 1 year ago 2 times by robl

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JohnR

(@johnr)

Estimable Member Member

Joined: 1 year ago

Posts: 106

30/11/2024 5:49 pm

Posted by: @didjerama_uk

↑

@graham-s Really useful to know, thank you. We have cavity wall insulation, suspended ground floor with no insultation, double glazing etc. however we aren't sure what the speciation of the system is designed for (in terms of heat loss). Our main concern is the buffer tank as it really not holding the heat and heating circuit seems to be lower than the set point of the buffer tank..

Is the buffer tank in the house? If so, any heat loss should be contributing to the domestic heating and, for the summer half the heat should be making the house too hot. Do you need the buffer tank to be that hot?

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didjerama_uk

(@didjerama_uk)

Active Member Member

Joined: 1 year ago

Posts: 4

Topic starter 05/12/2024 5:50 pm

@johnr Thanks - the Buffer tank is in the integral garage. We need the buffer tank to be that hot otherwise the house doesn't heat up. We have tried the buffer tank at a lower set point however it seems to make things worse.

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greenlight

(@greenlight)

Active Member Member

Joined: 9 months ago

Posts: 7

23/03/2025 10:38 pm

Once you have 3-5 degree delta t on brine side then that’s all that’s matters on the collector side.

If you are low on gas or poor antifreeze, you’ll get low pressure faults. Once you don’t get those, then just focus on the hot side. That’s where the money is saved

What matters on the heating and hot water is you just keep your flow temps down as low as possible.

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